Gas burners

ABSTRACT

A gas burner which provides between the exit orifices and the ignition level a free path for gas jets emanating from the orifices to ensure sufficient aeration of the gas jets. The burner comprises a casing connectible to a gas supply and having a number of gas exit orifices provided therein. Above these orifices there is provided a distributor body presenting a distribution wall inclined relative to the axes of the exit orifices and with its upper edge disposed at least approximately in the plane defined by the axis of the exit orifices. This edge forms part of a ledge whereof at least the major part is on the same side as the orifices and above the distribution wall. The ledge and distribution wall subtend an acute angle at said edge and the other edge of the ledge terminates in a low wall substantially perpendicular to the ledge and parallel with the edge.

United States Patent Vignes GAS BURNERS [72] Inventor: Roger Vignes, Paris, France [73] Assignee: Service National dit: Gaz de France,

Paris, France [22] Filed: April 30, 1971 [21] Appl.No.: 139,021

[30] Foreign Application Priority Data April 30, 1970 France ..701609O [52] US. Cl. ..43l/347, 431/350, 239/520, 239/521 [51] Int. Cl ..F23d 13/12 [58] Field of Search ..239/288.3, 499, 520, 521; 431/347, 350, 354

[56] References Cited UNITED STATES PATENTS 1,437,524 12/1922 Lee ..239/288.3 1,703,597 2/1929 Reeves ..431/350 X 1,931,589 10/1933 Roberts ..431/347 1 Aug. 29, 1972 2,260,166 lO/1941 Cope ..43l/347 X Primary ExaminerCarroll B. Dority, Jr.

Att0rneyMason, Fenwick & Lawrence [5 7 ABSTRACT A gas burner which provides between the exit orifices and the ignition level a free path for gas jets emanating from the orifices to ensure sufficient aeration of the gas jets. The burner comprises a casing connectible to a gas supply and having a number of gas exit orifices provided therein. Above these orifices there is provided a distributor body presenting a distribution wall inclined relative to the axes of the exit orifices and with its upper edge disposed at least approximately in the plane defined by the axis of the exit orifices. This edge forms part of a ledge whereof at least the major part is on the same side as the orifices and above the distribution wall. The ledge and distribution wall subtend an acute angle at said edge and the other edge of the ledge terminates in a low wall substantially perpendicular to the ledge and parallel with the edge.

18 Claims, 11 Drawing Figures PATENTEDnuszs 1912 SHEET 2 0F 4 Fig. 7

PATENTEDmczs I972 I 3.687.602 SHEEI u [1F 4 Fig. 7/

I m 0 I i 50 0 1000 13-00 T 0,35 0,52 0,60 0,75 0,88 0,90 gm d/mm V Invenlor 0652 V/mve's a A Horn e ys GAS BURNERS This invention relates to a gas burner of the type ensuring the mixture of air and gas by induction and diffusion produced around a jet of free gas and comprising a casing connected to a source of combustible gas, an appropriate number of gas exit orifices arranged in the casing and a distribution wall which at its upper part and opposite the exit orifices terminates in a ridge or edge, the wall being disposed above the casing with regard to the exit orifices and being inclined relative to the axes of the exit orifices.

In known burners of this type, the gas jets are directed towards the central or median part of the distribution wall, where they entirely collapse or spread out, so that the flames ignited on the distribution wall are diverted by the wall and burn along the wall which serves as a deflector.

According to a known method of burner construction of this type (US. Pat. No. 1,437,524), the distribution wall is located very near the gas exit orifices so that the aeration of the gas jets impinging on the wall is insufficient if one uses gas other than Town gas and particularly gases rich in hydrocarbons. On that account, there is produced on the distribution wall a carbonaceous deposit which renders the flame unstable and causes poor combustion of the gas. This inconvenience can be accepted when one only uses the burner sporadically, for example, to ignite combustible solids placed on a grille above this known burner.

In order to improve the aeration of the gas jet and so the combustion of the latter, it has already been proposed to increase the free distance (length) of the gas jet between the exit orifice and the distribution wall which is incurred so as to form a concave chamber open towards the gas jet (US. Pat. No. 2,310,116). The position of the distribution wall or concave chamber relative to the gas jet exit orifice is then adjusted so that the gas burns inside the concave chamber formed by the distribution wall. Here again, the combustion of the gas is bad and carbonaceous deposits are produced when gases rich in hydrocarbons are employed since the concave chamber partially impedes or blocks the access of the air to the location where the flames are initiated. Besides, due to the fact that the gas jet impinges wholly against the distribution wall, its kinetic energy and consequently that of the flame is almost entirely destroyed so that the parts of the flame leaving the concave chamber do not have sufficient impetus to overcomethe losses of pressure which they can encounter for example in an exchanger tube with a hairpin bend. Another serious inconvenience of this known burner resides in the fact that it produces wide and unstable flames which can only be aerated on their periphery.

The invention has for its object the mitigation or obviation of the aforesaid inconveniences and the realization of a burner of the type first-mentioned which permits the obtaining of correctly aerated and stabilized flames of compact form and presenting a sufficient impulsion to permit them to preserve their general direction whatever the inclination of the burner.

This object is attained, according to the invention, due to the fact that the top ridge or edge of the distribution wall is located at least approximately in the plane defined by the axes of the exit orifices and is adjacent a ledge whereof at least the major part is located on the same side of the axes of the exit orifice and above the distribution wall, the ledge, on the one hand, forming with the distribution wall, in a plane perpendicular to the ridge or edge, an acute angle, and, on the other hand, at the side opposite the ridge or edge being limited by a wall of small height which is at least approximately perpendicular to the plane of the ledge or edge and parallel with the ridge.

Due to this arrangement, the gas-air mixture is directed to the surface of the edge or ridge and the ledge of the distribution wall by tubulences which are created at this surface. The tubulences (eddies) overcome the speed of the jet of gas-air mixture, and when this mixture is ignited at the surface of the ledge, it burns with a stable flame which has an impulsion sufficient to burn with an elongate form substantially parallel to the plane of the ledge. As the flame itself is free on all sides, secondary air can flow thereto and ensure correct combustion without carbonization.

The object of the present invention will be better understood with the help of the following description of several exemplary embodiments and with the help of the accompanying exemplary drawings, in which:

FIG. 1 is a transverse sectional elevation of one embodiment of burner according to the invention;

FIG. 2 is a perspective view of a second embodiment;

FIG. 3 is a perspective view of a third embodiment;

FIG. 4 is a perspective view of a fourth embodiment;

FIG. 5 is a sectional view of a fifth embodiment;

FIG. 6 is a vertical sectional view on the line VI-VI of FIG. 7 through a burner particularly suitable for cooking;

FIG. 7 is a plan view of the burner shown in FIG. 6;

FIGS. 8 to 10 show in section and perspective modifications of the embodiments of FIGS. 1, 3 and 5, and

FIG. 11 is a graph showing the relationship between the different parameters of constructions of a burner according to the invention.

The burners shown in FIGS. 1 to 5 comprise a distributor body 1 associated with several gas exit orifices 2 formed in a casing 3 connected to a source of combustible gas.

The exit orifices 2 of small diameter, for example 0.3 to 2.5 mm are formed by any appropriate means in the upper part of the casing 3, constituted for example by a screwed coupling connected through the intermediary of a feed pipe to a source of combustible gas.

The exit orifices 2 are preferably disposed near the edge of the casing 3. The axis of the exit orifices 2 is, for example, parallel with the general axis of the burner and is disposed in a particular manner as will be explained later. The distributor body 1 is mounted, in appropriate manner, on the part of the casing 3 provided with the exit orifices 2. The distributor body 1 presents a distribution wall 4 inclined relative to the axis of the gas exit orifices 2 and has at the end remote from the exit orifices 2 a ridge or edge 7 followed by a ledge or shoulder 5 directed away from the plane defined by the axis of the exit orifices 2.

The ledge or shoulder 5 terminates remote from the top ridge or edge 7 of the distribution wall 4 in a wall 6 of slight height preferably perpendicular to the plane of the ledge 5. The height of the wall 6 terminating the ledge 5 is substantially equal to the width or depth of the ledge 5. The ledge determines with the upper extremity of the inclined distribution wall 4 the sharp ridge or edge 7 located in the plane or very near the plane defined by the axes of the exit orifices 2. In other words, when the axes of the exit orifices are vertical the sharp edge 7 is located straight above the exit orifices 2. The angle subtended at the ridge or edge 7 between the distribution wall 4 and the ledge 5 is an acute angle. The inclination of the distribution wall 4 relative to the axis of the exit orifices 2 is between 5 and 30, preferably As can be seen in FIG. 1, the distributor body 1 has a second distribution wall 4a disposed symmetrically relative to the plane of symmetry of the burner. Exit orifices 2a, a ledge or shoulder 5a and a low wall 6a are equally provided in symmetrical fashion relative to the plane of symmetry of the burner.

The functioning of the burner according to the invention is as follows: the jets 8 and 8a of pure gas leaving the exit orifices 2, 2a passes into the free air and partially strike at a small angle the upper part of the inclined distribution wall 4, 4a. There is thus assured a preliminary mixing of the ambient air and the combustible gas due to the phenomena of induction and diffusion produced around the lower zone of the gas jet; the path of the inducted air is indicated schematically in FIG. 1 by the arrows 9. Due to these phenomena there is obtained a well aerated gas jet.

The impact of the jets 8 and 8a of air-gas mixture on the upper part of the inclined distribution wall 4, 4a causes a spreading of the air-gas jet along the upper extremity of the inclined wall 4, 4a.

This spreading of the air-gas jet ensures the mixing and homogenization of the mixture. Moreover, this spreading facilitates the interignition of the different jets of mixture impinging on the upper part of the distribution wall 4, 40. Further, by differential braking of the different layers of jets of mixture, the gas-air mixture tends to adhere to the wall 4, 4a.

The air-gas mixture commences to burn at the level of the ledge or shoulder 5. The ledge 5 modifies the spreading of the gas-air mixture by creating a zone of turbulence in which the speed of circulation of the gasair mixture due to the kinetic energy of the jets of gas is practically cancelled out. Thus the flames are stabilized on the distributor body 1 and their roots are held at the level of the ledge 5 and the wall 6.

In other words, the flames are stabilized at the surface of the ledge 5 and the wall 6 by the phenomenon of retention.

The combustion of the air-gas mixture held at the level of the shoulder or ledge 5 creates a thermal draught directed towards the flame 10, 11 a secondary flow of air moving along the direction of the arrows 12 and bringing towards the center of the flame l0, 1 1, the air-gas mixture corresponding to the part of the gas jets elongated by the distribution wall 4, 4a.

The current of secondary air surrounds the flame 10, 111 at the holding location (ledge 5 and wall 6) and contributes to the aeration of the flame 10, 1 1 by diffusion.

The combustion zone is consequently stabilized at the level of the upper extremity of the distributor body 1 and initiates flames of the aerated type presenting a blue cone 10 and a plume 11.

The flames thus obtained are very aerated.

The air-gas mixture near the stoechiometric value initiates flames of slight volume, stable and turbulent.

In FIG. 1, the distributor body 1 is elongate perpendicularly with a section shown as a slope.

. On the contrary, in FIG. 2, there is shown a second embodiment of burner comprising a distributor body 1 of truncated form integral at its smaller end with a casing 3 is the form of a plinth closed at its upper face 3b and provided at its lower end with screw-threading 30 to permit its securement to a gas feed pipe.

The annular face at the side of the smaller end of the truncated distributor body 1 is provided with a certain number of gas exit orifices 2 disposed in a circle and located directly beneath the sharp edge 7 of the larger end of the truncated distributor body 1.

Inwardly relative to the sharp edge 7 of the larger end is provided a low cylindrical element 6 which delimits at the larger end of the distributor body 1 the annular ledge or shoulder 5.

The burner shown in FIG. 3 comprises a casing 3 in the form of a rectangular rail. This rail is for example, constituted by a flattened tube whereof the upper elongate surface is provided near one of its longitudinal edges with a series of exit orifices and near the other edge with a distributor body 1 formed by a metal sheet folded so as to provide, as in the preceding example, a distribution wall 4, a ledge 5, a low wall 6 and a sharp edge 7 located in the plane defined by the axes of the exit orifices 2. This burner can be completed by a second burner 1 which is disposed symmetrically relative to and adjacent the first (1) so that the rail faces 3, 3a provided with exit orifices 2, the distribution walls 4, 4a and the low walls 6, 6a are located opposite one another while the intermediate space 15 permits air to aerate the flames at the sides of the low walls 6, 6a. In this case also, the ledge 5a merges with the upper extremity of the distribution wall at the rectilinear sharp edge 7a and forms with the said wall 4a an acute angle.

According to a modification (not shown) the rail 3 as well as the distributor body constituted by the inclined walls 4, 4a, the ledges 5, 5a and the low walls 6, 6a parallel with the axes of the exit orifices can be provided in the form of an annulus or a coil.

In FIG. 4 there is shown a simple annular burner.

The casing is constituted by an annular tube 3 supporting on its inner edge the hollow distributor body 1 of truncated form.

The tube 3 is provided on its periphery with a feed pipe 13 which extends tangentially into the chamber defined by the annular tube 3 which has at its upper face, near its outer edge a series of exit orifices 2 disposed this time in a circle.

The distributor body 1 presents an inclined distribution wall 4 constituted by a metal sheet of truncated form whereof the smaller end is integral with the annular tube 3 within the circle defined by the series of exit orifices 2. At its upper end, the inclined distribution wall 4 has an annular ledge or shoulder 5 extending radially inwards and whereof the exterior edge constitutes the sharp edge 7 at the upper extremity of the inclined distribution wall. At its inner edge, the ledge 5 terminates in a low sheet metal wall 6 perpendicular to the plane of the ledge 5.

The sharp edge 7 is located vertically above the exit orifices or move precisely in the plane defined by the axes of the exit orifices 2.

The embodiment shown in FIG. 5 difiers from the previously described embodiments in that the axis of the exit orifices 2 is inclined relative to the plane or general axis of the burner. Preferably, the angle of inclination between the axis of the exit orifices and the distribution wall 4 is between 5 and 30 and is preferably Preferably, the upper and lower surfaces 3b, 3d of the top wall of the casing 3 are perpendicular to the axis of the exit orifices 2. Due to the inclination of the axes of the exit orifices 2, the burner can be conceived in a most compact manner, which is advantageous especially in installations which provide little space for mounting burners.

The upper end of the low wall 6 inwardly of the sharp edge 7 is provided with a flange 14 which is parallel to the ledge 5 and is rectilinear or annular depending on the general form of the burner, this flange 14 protruding slightly relative to the wall 6 to overly part of the shoulder or ledge 5. This flange 14 has, preferably, a width and a height between a quarter and a third of the height of the wall 6.

Due to this particular arrangement which can, besides, be equally combined with the other embodiments of the burner, there is enhanced still more the stability of the flames in difficult conditions. The general axis of the burners can have different inclinations relative to the vertical. The burners provided with a flange 14 even function correctly in horizontal disposition provided the pressure of the gas jets is sufficient.

In FIGS. 6 and 7, there is shown an embodiment particularly adapted for cooking. It is known that cooking burners must be controllable between certain limit values of gas pressure for heating purposes. If, in the case of the embodiments of FIGS. 1 to S and FIGS. 8 to 11), the gas pressure falls too much, the impact of the gas jet would be developed wholly on the distribution wall and the flames would no longer be held at the ledge but would burn directly on leaving the exit orifices and as a result the distribution wall would be exposed thereto. The poor aeration of such flames would give rise to carbonization.

To avoid these inconveniences, it is proposed according to the embodiment of FIGS. 6 and 7 to dispose the distributor body 1 underneath the inclined axes of the exit orifices 2 and not above as is shown in FIG. 5.

The distributor body 1 is annular with its internal face conical narrowing from top to bottom and serving as the distribution wall 4. The casing 3 is of cylindrical form terminating at its upper end in a conical wall 3b provided with exit orifices 2 whose axes are inclined relative to the vertical and coincide substantially with the upper edge or ridge 7 of the distribution wall 4. At its bottom, the casing 3 rests on a support plate 16 of a cooker (not shown) and is coupled to a feed pipe 13. The annulus 1 and the casing 3 as well as the edge 7 and circular series of exit orifices 2 are disposed coaxially and concentrically.

As can be seen from FIG. 6, the angle of inclination of the distribution wall 4 relative to the horizontal is greater than that of the axes of the exit orifices. In this embodiment, the angle subtended between the axes of the exit orifices 2 and the distribution wall is of the order of 10.

The annular distributor body 1 rests on support feet 17 fixed on the support plate 16. The support feet 17 maintain the distributor body at a certain distance from the exit orifices 2 and thus ensure that the ambient air has free access to the jets of gas leaving the orifices 2. It would be equally possible to fix the support feet 17 on the cylindrical part of the casing 3.

As in the preceding embodiments, the upper edge or ridge 7 is followed by a ledge 5 extending this time radially outwards so as to form a frustum of a cone converging towards the center and the top of the distributor body 1. The ledge 5 subtends with the distribution wall an acute angle for example of the order of and is, on its outer edge, adjacent the low wall 6 disposed at least nearly perpendicularly to the cone frustum defined by the ledge 5. The upper end of the wall 6 terminates in the upper truncated surface 1b of the distributor body 1, this surface 1b being substantially parallel to that of the ledge 5 and adapted to permit secondary air access to the flames 10, 11.

At normal pressure, the flames 10, 1 1 are well held at 5, 6 on the distributor body 1. When the pressure falls, the flames initiate at the exit of the orifices 2 and are adjusted or corrected under the eflect of air entering the distributor body in the region of the space 18 between the upper part 3b of the casing 3 and the lower part of the distributor body 1 (see flames 10a, 11a in dotted lines). In this manner, this construction of burner can be also used without inconvenience with very feeble outputs of gas.

The embodiments shown in FIGS. 8 to 10 are constructed similarly to those of FIGS. 1, 3 and 5 with the difference that the distribution walls 4, 4a are so near one another (FIGS. 8 and 9) or the distribution wall 4 has such an inclination relative to the axis of the casing 3, that they cannot be directly fixed on the casing if one Ll wrshes to marntarn and appropriate distance between the exit orifices 2 and the edge 7, a distance L] T whose functron wrll be explarned later.

Thus it is proposed to extend the distribution walls 4, 4a at the bottom by an extension piece 19 in the form of a solid body thick or thin, parallelipiped or cylindrical, perforated or not depending on the form of the distributor body 1, the extension piece 19 being perpendicular to the upper face 3b of the casing 3.

In FIG. 8, the extension piece 19 integral with the upper wall 3b of the casing 3 has a parallelipiped form whereof the two lateral walls 19a, 19b subtend an obtuse angle with the distribution walls 4, 4a and are parallel to the axes of the exit orifices 2. The extension piece 19 can, besides, be grooved or channeled over all its height and a major part of its length.

The embodiment of FIG. 9 has distribution walls 4, 4a very close together at their surfaces remote from the corresponding exit orifices 2, 2a and are fixed on their corresponding rails 3, 3a by extension legs 19c preferably disposed between two adjacent orifices 2 or 2a. The rails 3, 3a can be unitary.

According to FIG. 10, the exit orifices 2 formed in the upper wall 3b of the casing 3 and perpendicularly to the lower face 3d and upper face of the said wall 3b are inclined relative to the vertical so as to define generatrices of a cone whose apex is at the bottom. The axes of the exit orifices 2 coincide with the periphery of the inverted cone which constitutes the distributor body 1. The circumference of the large base of the cone 1 constitutes the sharp edge 7 from which extends radially inwards an annular ledge 5. At the inner edge, the ledge S terminates on a low wall 6 and an annular flange l4 overlies the ledge 5. Near its apex the conical distributor body 1 is cut and fixed on the extension piece 19 of cylindrical form which is itself integral with the upper wall 3b of the casing 3 within a circle defined by the series of exit orifices 2.

The graph shown in FIG. 11 shows at the X-axis the calorific output Qc in millitherms/hour as well as the internal diameter of the gas exit orifices 2 or 2a in millimeters and at the Y-axis the lengths in millimeters of the difierent parameters of the distributor body 1 which is equally schematically shown in FIG. 1 I.

The gas used for the different values indicated in this graph is the natural gas of LACQ employed with a suppression of 18 millibars.

The curves L1, L2, L3, L4 indicate respectively the distance between the exit orifice 2 and the sharp edge 7, the distance between the two adjacent orifices 2 and 2a, the height of the wall 6 opposite the sharp edge 7 and terminating the ledge S, and the width of the ledge 5.

Besides, the distributor bodies employed to establish this graph have distribution walls 4 inclined at 10 relative to the axis of the exit orifices.

From this graph it can be seen that the width of the ledge 5 and the height of the wall 6 terminating the said ledge 5 are substantially equal to one another, the distance between two adjacent orifices 2 is equal to three or four times the width of the ledge or shoulder 5 and the distance between an exit orifice 2 and the sharp edge or ridge 7 is equal to eight or nine times the width of the ledge.

Moreover, a man versed in the art will easily and readily determine from the preceding description other parameters, for example that the distribution wall 4 forms with the axis of the exit orifices angles other than 10.

The present invention covers modifications when departing from the scope of the claimed invention.

WHAT IS CLAIMED IS:

1. A gas burner of the type ensuring air and gas mixture by induction and diffusion around a jet of free gas and comprising a casing connected to a source of combustible gas, a number of gas exit orifices provided in the casing and a distribution wall inclined relative to the axes of the exit orifices and which at its upper end and opposite the exit orifices terminates in an edge disposed above the casing and the exit orifices, the upper edge of the distribution wall being located at least approximately in the path defined by the axes of the exit orifices and being adjacent a ledge whereof at least the major part of the ledge is disposed to one side of said part and above the distribution wall, the said ledge subtending an acute angle with the distribution wall at said edge, and said ledge at the side opposite the edge terminating in a low wall which is at least approximately perpendicular to the ledge and parallel to the edge.

2. A burner according to claim 1, in which the distribution wall subtends with the axis of the exit orifices an acute angle between 5 and 30, preferably 10.

3. A burner according to claim 1 in which the distribution wall presents a plain surface and has a rectilinear ledge adjacent its upper edge, the distribution wall resting on a casing connected to a feed pipe for combustible gas and being in the form of a hollow rail provided with a number of exit orifices aligned in a straight line with the sharp edge of the distribution wall.

4. A burner according to claim 1 comprising two distribution walls inclined relative to one another and converging towards the casing, which is provided with two rows of exit orifices, whereof the axes coincide with the sharp edge of the corresponding distribution walls, the ledges and the low walls being rectilinear and directed away from the axes of the orifices and the distribution wall being located opposite the corresponding orifices.

5. A burner according to claim 1 in which the distribution wall is constituted by a truncated cone, whereof the small end is fixed on the upper surface of the casing and whereof the large end provides, at its outer edge, the sharp edge coinciding with the axes of the gas exit orifices which are disposed in a circle in the upper surface of the casing, the ledge extending inwardly from the external edge of the large end of the truncated cone and being of annular form and terminating at its other edge in a low cylindrical wall.

6. A burner according to claim 1 in which the distribution wall is constituted by a solid member.

7. A burner according to claim 1 in which the distribution wall is constituted by sheet metal.

8. A burner according to claim 1, in which the distribution wall, the ledge and the low cylindrical wall are annular.

9. A burner according to claim 1, in which the exit orifices are provided in the upper surface of the casing which is in the form of a hollow annular rail supporting inside the circle of orifices a distribution wall of truncated form and being coupled at its periphery to a feed pipe which extends tangentially into the chamber defined by the annular rail.

10. A burner according to claim 1 in which the low wall remote from the sharp edge of the distribution wall is provided at its upper end with a flange protruding slightly out from the low wall so as to overly part of the ledge.

11. A burner according to claim 1 in which the distribution wall is disposed outside and beneath the axes of the exit orifices coinciding with the sharp edge of the distribution wall, the lower end of the distribution wall being spaced from the exit orifices so as to allow free access of air to the orifices.

12. A burner according to claim 1, in which the distribution wall the ledge and the low wall constitute internal faces of a ring and form truncated cones, whereof the axes are coaxial to the axis of the upper conical surface of the casing and the circular series of exit orifices formed in said upper surface, the axes of the exit orifices defining generatrices of a cone whereof the base coincides with that of the distribution wall and which is located inside the cone determined by the distribution wall, the distribution wall being fixed by support feet to a support surface to provide a passage for air between the lower end of the distribution wall and the upper surface of the casing.

13. A burner according to claim 1 in which the lower end of the distribution wall is fixed on the casing through the intermediary of an extension member whereof the external face forms an obtuse angle with the distribution wall.

at least three times the width of the ledge.

17. A burner according to claim 1 in which the distance between an exit orifice and the sharp edge is equal to at least eight times the width of the ledge.

18. A burner according to claim 1 to 17, in which the axes of the exit orifices is inclined relative to the general axis of the burner. 

1. A gas burner of the type ensuring air and gas mixture by induction and diffusion around a jet of free gas and comprising a casing connected to a source of combustible gas, a number of gas exit orifices provided in the casing and a distribution wall inclined relative to the axes of the exit orifices and which at its upper end and opposite the exit orifices terminates in an edge disposed above the casing and the exit orifices, the upper edge of the distribution wall being located at least approximately in the path defined by the axes of the exit orifices and being adjacent a ledge whereof at least the major part of the ledge is disposed to one side of said part and above the distribution wall, the said ledge subtending an acute angle with the distribution wall at said edge, and said ledge at the side opposite the edge terminating in a low wall which is at least approximately perpendicular to the ledge and parallel to the edge.
 2. A burner according to claim 1, in which the distribution wall subtends with the axis of the exit orifices an acute angle between 5* and 30*, preferably 10*.
 3. A burner according to claim 1 in which the distribution wall presents a plain surface and has a rectilinear ledge adjacent its upper edge, the distribution wall resting on a casing connected to a feed pipe for combustible gas and being in the form of a hollow rail provided with a number of exit orifices aligned in a straight line with the sharp edge of the distribution wall.
 4. A burner according to claim 1 comprising two distribution walls inclined relative to one another and converging towards the casing, which is provided with two rows of exit orifices, whereof the axes coincide with the sharp edge of the corresponding distribution walls, the ledges and the low walls being rectilinear and directed away from the axes of the orifices and the distribution wall being located opposite the corresponding orifices.
 5. A burner according to claim 1 in which the distribution wall is constituted by a truncated cone, whereof the small end is fixed on the upper surface of the casing and whereof the large end provides, at its outer edge, the sharp edge coinciding with the axes of the gas exit orifices which are disposed in a circle in the upper surface of the casing, the ledge extending inwardly from the external edge of the large end of the truncated cone and being of annular form and terminating at its other edge in a low cylindrical wall.
 6. A burner according to claim 1 in which the distribution wall is constituted by a solid member.
 7. A burner according to claim 1 in which the distribution wall is constituted by sheet metal.
 8. A burner according to claim 1, in which the distribution wall, the ledge and the low cylindrical wall are annular.
 9. A burner according to claim 1, in which the exit orifices are provided in the upper surface of the casing which is in the form of a hollow annular rail supporting inside the circle of orifices a distribution wall of truncated form and being coupled at its periphery to a feed pipe which extends tangentially into the chamber defined by the annular rail.
 10. A burner according to claim 1 in which the low wall remote from the sharp edge of the distribution wall is provided at its upper end with a flange protruding slightly out from the low wall so as to overly part of the ledge.
 11. A burner according to claim 1 in which the distribution wall is disposed outside and beneath the axes of the exit orifices coinciding with the sharp edge of the distribution wall, the lower end Of the distribution wall being spaced from the exit orifices so as to allow free access of air to the orifices.
 12. A burner according to claim 1, in which the distribution wall the ledge and the low wall constitute internal faces of a ring and form truncated cones, whereof the axes are coaxial to the axis of the upper conical surface of the casing and the circular series of exit orifices formed in said upper surface, the axes of the exit orifices defining generatrices of a cone whereof the base coincides with that of the distribution wall and which is located inside the cone determined by the distribution wall, the distribution wall being fixed by support feet to a support surface to provide a passage for air between the lower end of the distribution wall and the upper surface of the casing.
 13. A burner according to claim 1 in which the lower end of the distribution wall is fixed on the casing through the intermediary of an extension member whereof the external face forms an obtuse angle with the distribution wall.
 14. A burner according to claim 13, in which the extension member is constituted by legs fixed on the casing between two adjacent orifices.
 15. A burner according to claim 1 in which the width of the ledge and the height of the wall limiting the ledge at the side opposite the sharp edge are substantially equal to one another.
 16. A burner according to claim 1 in which the distance between two adjacent exit orifices is equal to at least three times the width of the ledge.
 17. A burner according to claim 1 in which the distance between an exit orifice and the sharp edge is equal to at least eight times the width of the ledge.
 18. A burner according to claim 1 to 17, in which the axes of the exit orifices is inclined relative to the general axis of the burner. 